Cilostazol (Page 3 of 4)

12.2 Pharmacodynamics

Cilostazol’s effects on platelet aggregation were evaluated in both healthy subjects and in patients with stable symptoms of cerebral thrombosis, cerebral embolism, transient ischemic attack, or cerebral arteriosclerosis over a range of doses from 50 mg every day to 100 mg three times a day. Cilostazol significantly inhibited platelet aggregation in a dose-dependent manner. The effects were observed as early as 3 hours post-dose and lasted up to 12 hours following a single dose. Following chronic administration and withdrawal of cilostazol, the effects on platelet aggregation began to subside 48 hours after withdrawal and returned to baseline by 96 hours with no rebound effect. A cilostazol dosage of 100 mg twice daily consistently inhibited platelet aggregation induced with arachidonic acid, collagen and adenosine diphosphate (ADP). Bleeding time was not affected by cilostazol administration.

Effects on circulating plasma lipids have been examined in patients taking cilostazol. After 12 weeks, as compared to placebo, cilostazol 100 mg twice daily produced a reduction in triglycerides of 29.3 mg/dL (15%) and an increase in HDL-cholesterol of 4.0 mg/dL (≅ 10%).

Drug Interactions
Aspirin
Short-term (less than or equal to 4 days) coadministration of aspirin with cilostazol increased the inhibition of ADP- induced ex vivo platelet aggregation by 22% to 37% when compared to either aspirin or cilostazol alone. Short-term (less than or equal to 4 days) coadministration of aspirin with cilostazol increased the inhibition of arachidonic acid-induced ex vivo platelet aggregation by 20% compared to cilostazol alone and by 48% compared to aspirin alone. However, short- term coadministration of aspirin with cilostazol had no clinically significant impact on PT, aPTT, or bleeding time compared to aspirin alone. Effects of long-term coadministration in the general population are unknown.

In eight randomized, placebo-controlled, double-blind clinical trials, aspirin was coadministered with cilostazol to 201 patients. The most frequent doses and mean durations of aspirin therapy were 75 to 81 mg daily for 137 days (107 patients) and 325 mg daily for 54 days (85 patients). There was no apparent increase in frequency of hemorrhagic adverse effects in patients taking cilostazol and aspirin compared to patients taking placebo and equivalent doses of aspirin.

Warfarin
Cilostazol did not inhibit the pharmacologic effects (PT, aPTT, bleeding time, or platelet aggregation) of R- and S- warfarin after a single 25-mg dose of warfarin. The effect of concomitant multiple dosing of warfarin and cilostazol on the pharmacodynamics of both drugs is unknown.

12.3 Pharmacokinetics

Cilostazol is absorbed after oral administration. A high fat meal increases absorption, with an approximately 90% increase in C max and a 25% increase in AUC. Absolute bioavailability is not known. Cilostazol is extensively metabolized by hepatic cytochrome P-450 enzymes, mainly 3A4, and, to a lesser extent, 2C19, with metabolites largely excreted in urine. Two metabolites are active, with one metabolite appearing to account for at least 50% of the pharmacologic (PDE III inhibition) activity after administration of cilostazol.

Pharmacokinetics are approximately dose proportional. Cilostazol and its active metabolites have apparent elimination half-lives of about 11 to 13 hours. Cilostazol and its active metabolites accumulate about 2-fold with chronic administration and reach steady state blood levels within a few days. The pharmacokinetics of cilostazol and its two major active metabolites were similar in healthy subjects and patients with intermittent claudication due to peripheral arterial disease (PAD). Figure 1 shows the mean plasma concentration-time profile at steady state after multiple dosing of cilostazol 100 mg twice daily.

Distribution
Cilostazol is 95 to 98% protein bound, predominantly to albumin. The binding for 3,4-dehydro-cilostazol is 97.4% and for 4´-trans-hydroxy-cilostazol is 66%. Mild hepatic impairment did not affect protein binding. The free fraction of cilostazol was 27% higher in subjects with renal impairment than in healthy volunteers. The displacement of cilostazol from plasma proteins by erythromycin, quinidine, warfarin, and omeprazole was not clinically significant.

Metabolism
Cilostazol is eliminated predominantly by metabolism and subsequent urinary excretion of metabolites. Based on in vitro studies, the primary isoenzymes involved in cilostazol’s metabolism are CYP3A4 and, to a lesser extent, CYP2C19. The enzyme responsible for metabolism of 3,4-dehydro-cilostazol, the most active of the metabolites, is unknown.

Following oral administration of 100 mg radiolabeled cilostazol, 56% of the total analytes in plasma was cilostazol, 15% was 3,4-dehydro-cilostazol (4 to 7 times as active as cilostazol), and 4% was 4´-trans-hydroxy-cilostazol (20% as active as cilostazol).

Elimination
The primary route of elimination was via the urine (74%), with the remainder excreted in feces (20%). No measurable amount of unchanged cilostazol was excreted in the urine, and less than 2% of the dose was excreted as 3,4-dehydro- cilostazol. About 30% of the dose was excreted in urine as 4´-trans-hydroxy-cilostazol. The remainder was excreted as other metabolites, none of which exceeded 5%. There was no evidence of induction of hepatic microenzymes.

Special Populations
Age and Gender
The total and unbound oral clearances, adjusted for body weight, of cilostazol and its metabolites were not significantly different with respect to age (50 to 80 years) or gender.

Smokers
Population pharmacokinetic analysis suggests that smoking decreased cilostazol exposure by about 20%.

Hepatic Impairment
The pharmacokinetics of cilostazol and its metabolites were similar in subjects with mild hepatic disease as compared to healthy subjects.

Patients with moderate or severe hepatic impairment have not been studied.

Renal Impairment
The total pharmacologic activity of cilostazol and its metabolites was similar in subjects with mild to moderate renal impairment and in healthy subjects. Severe renal impairment increases metabolite levels and alters protein binding of the parent. The expected pharmacologic activity, however, based on plasma concentrations and relative PDE III inhibiting potency of parent drug and metabolites, appeared little changed. Patients on dialysis have not been studied, but, it is unlikely that cilostazol can be removed efficiently by dialysis because of its high protein binding (95 to 98%).

Drug Interactions
Cilostazol does not appear to inhibit CYP3A4.

Warfarin
Cilostazol did not inhibit the metabolism of R- and S-warfarin after a single 25-mg dose of warfarin.

Clopidogrel
Multiple doses of clopidogrel do not significantly increase steady state plasma concentrations of cilostazol.

Strong Inhibitors of CYP3A4
A priming dose of ketoconazole 400 mg (a strong inhibitor of CYP3A4), was given one day prior to coadministration of single doses of ketoconazole 400 mg and cilostazol 100 mg. This regimen increased cilostazol C max by 94% and AUC by 117%. Other strong inhibitors of CYP3A4, such as itraconazole, voriconazole, clarithromycin, ritonavir, saquinavir, and nefazodone would be expected to have a similar effect [see Dosage and Administration ( 2.2), Drug Interactions ( 7.1)].

Moderate Inhibitors of CYP3A4
Erythromycin and other macrolide antibiotics: Erythromycin is a moderately strong inhibitor of CYP3A4. Coadministration of erythromycin 500 mg every 8h with a single dose of cilostazol 100 mg increased cilostazol C max by 47% and AUC by 73%. Inhibition of cilostazol metabolism by erythromycin increased the AUC of 4´-trans-hydroxy- cilostazol by 141% [see Dosage and Administration ( 2.2)].

Diltiazem:
Diltiazem 180 mg decreased the clearance of cilostazol by ~30%. Cilostazol C max increased ~30% and AUC increased ~40% [see Dosage and Administration ( 2.2)].

Grapefruit Juice:
Grapefruit juice increased the C max of cilostazol by ~50%, but had no effect on AUC.

Inhibitors of CYP2C19
Omeprazole: Coadministration of omeprazole did not significantly affect the metabolism of cilostazol, but the systemic exposure to 3,4-dehydro-cilostazol was increased by 69%, probably the result of omeprazole’s potent inhibition of CYP2C19 [see Dosage and Administration ( 2.2)].

Quinidine
Concomitant administration of quinidine with a single dose of cilostazol 100 mg did not alter cilostazol pharmacokinetics.

Lovastatin
The concomitant administration of lovastatin with cilostazol decreases cilostazol C ss, max and AUCτ by 15%. There is also a decrease, although nonsignificant, in cilostazol metabolite concentrations. Coadministration of cilostazol with lovastatin increases lovastatin and ß-hydroxylovastatin AUC approximately 70% and is not expected to be clinically significant.

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